Where a person is charged in England or Wales before a magistrates' court with an offence under section 2 or with an offence under section 17, and the court is of opinion that the offence is not proved, then, at any time during the hearing or immediately thereafter the court may, without prejudice to any other powers possessed by the court, direct or allow a charge for an offence under section 3 or, as the case may be, section 18 to be preferred forthwith against the defendant and may thereupon proceed with that charge, so however that he or his solicitor or counsel shall be informed of the new charge and be given an opportunity, whether by way of cross-examining any witness whose evidence has already been given against the defendant or otherwise, of answering the new charge, and the court shall, if it considers that the defendant is prejudiced in his defence by reason of the new charge's being so preferred, adjourn the hearing.